1. Technical Field
Embodiments of the present invention relate to a fixing device to fix an image on a recording medium and an image forming apparatus including the fixing device.
2. Description of the Related Art
Image forming apparatuses are used as, for example, copiers, printers, facsimile machines, and multi-functional devices having at least one of the foregoing capabilities. As one type of image forming apparatus, electrophotographic image forming apparatuses are known. Such electrophotographic image forming apparatuses may have a fixing device to fix a toner image on a sheet of paper serving as a recording medium.
Such a fixing device includes, for example, a fixing rotary body heated by a heating member and an opposed member to contact the fixing rotary body. The fixing rotary body and the opposed member contact each other to form a nipping portion. When a sheet having a toner image passes through the nipping portion, toner is fused under the heat of the fixing rotary body and fixed on the sheet.
Typically, such a heating member heats the fixing rotary body over an entire width of the sheet passing the nipping portion. As a result, the entire sheet is heated by the fixing rotary body. However, when an image is placed on only a portion of the sheet, heat energy is wasted in a non-image area, i.e., an area having no image.
To reduce such waste of heat energy in the non-image area, for example, JP-2001-343860-A proposes a fixing device using, as an external heater, a thermal heater in which heaters are arranged at even spaces in the width direction of a sheet (see paragraph [0051] and FIGS. 11 and 12). By controlling each heater in accordance with image information, the fixing device adjusts a heating area in accordance with the distribution of an image area and a non-image area on a recording medium to heat the image area without heating the non-image area.
As described above, for the fixing device that adjusts the heating area in response to the distribution of an image area and a non-image area in an image, typically, the non-image area is maintained at a default constant temperature. However, such a configuration imposes a limitation on the effect obtained by the heating member that includes plural heaters arranged in the width direction of a sheet. The heating member thus configured has a potentiality to further enhance the multifunctionality of a fixing device.